1. Field of the Invention
The present invention primarily relates to a device for puncturing hard tissue in, for example, humans or animals, and to a technique for puncturing in this type of tissue.
The skeleton is the site of many different pathological lesions, blood diseases etc. The lesions are often visible on X-rays of the skeleton, but in general, it is not possible, using X-ray, to determine the cause of the lesion. In order to with certainty determine the nature of the lesion, parts of the bone must be removed and examined under microscope.
Biopsy sampling of the bone is difficult to perform due to the fact that the lesion is often surrounded by the hard outer surface of the bone known as corticalis.
2. Discussion of the Related Art
One way to gain access to the lesion through the cortical bone is to introduce a conventional spiral drill equipped with a cannula, drill through the cortical bone, then remove the drill. The cannula remains in place in the soft tissue, but cannot be inserted through the drilled hole in the cortical bone because the outer diameter of the cannula is larger than the diameter of the drilled hole. The disadvantage is that the cannula can easily be moved out of position, making it difficult to relocate the drilled hole in order to, for example, introduce a biopsy needle. This disadvantage is especially apparent when performing a puncture not at a right angle to the bone surface.
Currently, two main methods are used to obtain biopsy samples of bone: operative biopsy and percutaneous needle biopsy. An operative procedure often yields good results but requires general anesthesia as well as substantial resources and cost. Percutaneous needle biopsy is performed under a local anaesthetic. The needle usually consists of a sharpened or saw-toothed sampling cannula which is introduced into the lesion resulting in the excision of a biopsy sample. Upon introduction, a stylet is inserted into the cannula forming a sharp distal tip in order to facilitate entry into the soft tissue. Examples of this type of needle are described in European Pat. No. 0,296,421 (the Ostycut needle) and in U.S. Pat. No. 3,628,524 (the Jamshidi needle).
Existing needle biopsy methods have the substantial disadvantage of not being able to easily penetrate cortical bone. Common biopsy needles such as, for example, Jamshidi and Ostycut all have a needle tip which can only penetrate thin or soft cortical bone. This is due to the fact that the tip does not clear away the material like a drill, but instead wedges itself in using considerable insertion force combined with rotation. A further disadvantage is that the substantial friction which results between the needle and the cortical bone hinders the manipulation of the needle towards the target and causes development of heat which can be painful to the patient. Also common are needle types in which the distal end of the cannula is saw-toothed. Examples of this type of needle are described in U.S. Pat. No. 4,306,570 (the Corb needle). The disadvantage of the saw-teeth, however, is that the teeth become plugged with drill chips when the depth of the cut exceeds the length of the teeth.
Furthermore, the saw-teeth must be covered by an outer protective cannula upon insertion into the soft tissue of the body in order to avoid damage. This increases the requisite outer diameter of the needle.
Drills and drill units for making holes having a greater diameter than the diameter of the drill itself are as such, already in existence (see, for example, U.S. Pat. Nos. 4,635,738, 4,878,794, 5,009,271). These patents concern primarily drilling in the earth, for example, for oil, and lie therefore outside the technical area dealt with by the present invention.